Field application of selective precipitation for recovering Cu and Zn in drainage discharged from an operating mine

Resource Utilization of Acid Mine Drainage (AMD): A Review

Acid mine drainage (AMD) is a typical type of pollution originating from complex oxidation interactions that occur under ambient conditions in abandoned and active mines. AMD has high acidity and contains a high concentration of heavy metals and metalloids, posing a serious threat to ecological systems and human health. Over the years, great progress has been made in the prevention and treatment of AMD. Remediation approaches like chemical neutralization precipitation, ion exchange, membrane separation processes, and bioremediation have been extensively reported. Nevertheless, some limitations, such as low efficacy, excessive consumption of chemical reagents, and secondary contamination restrict the application of these technologies. The aim of this review was to provide updated information on the sustainable treatments that have been engaged in the published literature on the resource utilization of AMD. The recovery and reuse of valuable resources (e.g., clean water, sulfuric acid, and metal ions) from AMD can offset the cost of AMD remediation. Iron oxide particles recovered from AMD can be applied as adsorbents for the removal of pollutants from wastewater and for the fabrication of effective catalysts for heterogeneous Fenton reactions. The application of AMD in beneficiation fields, such as activating pyrite and chalcopyrite flotation, regulating pulp pH, and leaching copper-bearing waste rock, provides easy access to the innovative utilization of AMD. A review such as this will help researchers understand the progress in research, and identify the strengths and weaknesses of each treatment technology, which can help shape the direction of future research in this area.

Effective co-treatment of synthetic acid mine drainage and domestic sewage using multi-unit passive treatment system supplemented with silage fermentation broth as carbon source

A multi-unit passive treatment system was constructed for co-treatment of synthetic acid mine drainage (AMD) and domestic sewage supplemented with silage fermentation broth as carbon source. AMD and domestic sewage mixing pretreatment (unit 1) improved influent quality with pH increase, metals removal and nutrients supplement. The generated metal-rich sludge in unit 1 retained the metals (69.95% of Fe, 97.36% of Cu, 96.53% of Cd, 72.52% of Zn, and 8.59% of Mn) of influent prior to entering subsequent bioreactors. Silage fermentation broth performed well to promote bacterial sulfate reduction in sulfate reducing bioreactor system (unit 2). Residual metals (Mn) and organic/nutrient pollutants were further polished in surface-flow aerobic wetland (unit 3), where relatively high pH (7.4-8.6), aerobic condition, potential Mn-oxidizing bacteria, limestone layer and low concentrations of Fe(II) (0.04-3.5 mg/L) favored the efficient removal of Mn. After 210-day continuous flow-through experiment, this passive treatment system demonstrated the efficient performance, increasing pH from 2.5 to 8.0 with removal of metals (99%), sulfate and organic/nutrient pollutants. Diverse sulfate reducing bacteria including complete organic oxidizers (e.g. Desulfobacter) and incomplete organic oxidizers (e.g. Desulfovibrio) promoted sulfate reduction and organic/nutrient pollutants removal. Ammonia oxidizing bacteria (e.g. Nitrosomonas) and nitrite oxidizing bacteria (e.g. unidentified_Nitrospiraceae) were the potential nitrifiers for ammonia removal. Collaboration of anaerobic denitrifiers (e.g. Denitratisoma) and potential heterotrophic nitrifying and aerobic denitrifiers (HN-AD) achieved effective nitrate removal. This multi-unit treatment system with domestic sewage and silage fermentation broth as stimulation substrates provided an attractive option for AMD treatment.

Improved Pb(II) removal in aqueous solution by sulfide@biochar and polysaccharose-FeS@ biochar composites: Efficiencies and mechanisms

Novel biochars, namely nano iron sulfide@ walnut shell biochar (FeS@WNS), Starch-FeS@WNS and Chitosan-FeS@WNS, were prepared by WNS loaded with nano FeS and starch (or chitosan). Nano FeS can be effectively improved lead ions (Pb(II)) removal and starch (or chitosan) improved the stability of FeS and the defect of easy agglomeration. The materials were characterized by SEM, EDS, FTIR and XRD, and the preparation was successful. The adsorption capacity of Pb(II) reached 63.5, 80.0, 84.7 mg g^-1 under 0.5 g L^-1 of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS. The adsorption of Pb(II) on the materials was more consistent with the pseudo-second-order kinetic model (K₂ = 0.001-0.005 g (mg·min)^-1, R² = 0.980-0.999) and Langmuir model (R² = 0.974-1.00), indicating that the adsorption of Pb(II) was mainly monolayer adsorption dominated by chemical adsorption. △G < 0 (-3.7~-6.97) and △H > 0 (1.56-20.49) indicated that the reaction was a spontaneous endothermic process. The mechanisms of Pb(II) removal from aqueous solutions involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange and oxidoreduction. Additionally, stability and reusability of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS was good. The novel sorbents of Starch-FeS@WNS and Chitosan-FeS@WNS can be used in Pb(II) wastewater treatment.

High efficiency removal of Pb(ii) in aqueous solution by a biochar-supported nanoscale ferrous sulfide composite

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution. The experimental results of SEM, EDS, XRD, and FT-IR spectroscopy clearly implied that the biochar was successfully modified with nanoscale ferrous sulfide composite. The maximum adsorption capacity of Pb(ii) ions by FeS@biochar reached 88.06 mg g⁻¹. Compared with other reported adsorbents, the removal rate of Pb(ii) ions by FeS@biochar was higher. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the experimental adsorption results. The removal rate of Pb(ii) ions by FeS@biochar was controlled by the chemical reaction and monolayer adsorption on the surface of FeS@biochar. The mechanisms of Pb(ii) removal from aqueous solutions by biochar involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange, and chemical precipitation. Additionally, the chemical stability and reusability of FeS@biochar were good. It is also an environment-friendly material for low-cost wastewater treatment.

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution.

Kinetics and mechanisms of the interaction between the calcite (10.4) surface and Cu2+-bearing solutions

Calcite dissolution, occurring in rocks, soils and sediments, is essential to indicate element cycles and local environments in the lithosphere, biosphere, hydrosphere and atmosphere. Calcite dissolution strongly depends on metal ions in aqueous solutions. Previous studies showed that aquatic Cu²⁺, a typical bio-toxic metal ion, can alter the calcite dissolution behavior. However, wide concentration ranges of Cu²⁺ coexisting with ubiquitous anions in local environments, such as waterways in the oxidation zones of copper deposits and soils near metal processing industry, was overlooked. When a considerable amount of aquatic Cu²⁺ ions are released into the environment, they migrate, diffuse, and hence become an environmental pollutant. Therefore, we focused on the interaction between calcite dissolution and wide concentration ranges of Cu²⁺-bearing solutions with different types of anions (SO₄^2-, Cl^- and NO₃^-). Comprehensive approaches including in situ atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and density functional theory (DFT) calculations were employed to investigate kinetics and mechanisms of the interaction between the calcite (10.4) surface and Cu²⁺-bearing solutions. Results demonstrated that both anion types and Cu²⁺ concentrations dramatically affect calcite dissolution. The morphology of etch pits generated in CuSO₄ solutions can be fan-shaped but changed to tear-shaped in Cu(NO₃)₂ or CuCl₂ solutions. Calcite dissolution kinetics is inhibited at c_Cu2+ ≤ 0.1 mM, caused by the coverage of active sites on calcite surfaces. As the Cu²⁺ concentration increases (1 mM ≤ c_Cu2+ ≤ 10 mM), calcite dissolution kinetics is enhanced due to the coupling effect of Cu²⁺-incorporated surface structure and solution chemistry. These results revealed the interactive mechanism between calcite dissolution and the migration of toxic Cu²⁺ in waterways, provided a practical consideration in dealing with the local environment.

A critical review on remediation, reuse, and resource recovery from acid mine drainage

Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.